Re: [PATCH 5/8] mm/kasan, mm/vmalloc: Respect GFP flags in kasan_populate_vmalloc()

[Andrey Ryabinin <ryabinin.a.a@gmail.com>]

On 8/7/25 9:58 AM, Uladzislau Rezki (Sony) wrote:

> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index d2c70cd2afb1..5edfc1f6b53e 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -335,13 +335,13 @@ static void ___free_pages_bulk(struct page **pages, int nr_pages)
>  	}
>  }
>  
> -static int ___alloc_pages_bulk(struct page **pages, int nr_pages)
> +static int ___alloc_pages_bulk(struct page **pages, int nr_pages, gfp_t gfp_mask)
>  {
>  	unsigned long nr_populated, nr_total = nr_pages;
>  	struct page **page_array = pages;
>  
>  	while (nr_pages) {
> -		nr_populated = alloc_pages_bulk(GFP_KERNEL, nr_pages, pages);
> +		nr_populated = alloc_pages_bulk(gfp_mask, nr_pages, pages);
>  		if (!nr_populated) {
>  			___free_pages_bulk(page_array, nr_total - nr_pages);
>  			return -ENOMEM;
> @@ -353,25 +353,33 @@ static int ___alloc_pages_bulk(struct page **pages, int nr_pages)
>  	return 0;
>  }
>  
> -static int __kasan_populate_vmalloc(unsigned long start, unsigned long end)
> +static int __kasan_populate_vmalloc(unsigned long start, unsigned long end, gfp_t gfp_mask)
>  {
>  	unsigned long nr_pages, nr_total = PFN_UP(end - start);
> +	bool noblock = !gfpflags_allow_blocking(gfp_mask);
>  	struct vmalloc_populate_data data;
> +	unsigned int flags;
>  	int ret = 0;

gfp_mask = (gfp_mask & GFP_RECLAIM_MASK);


But it might be better to do this in alloc_vmap_area().
In alloc_vmap_area() we have this:

retry:
	if (IS_ERR_VALUE(addr)) {
		preload_this_cpu_lock(&free_vmap_area_lock, gfp_mask, node);

which probably needs GFP_RECLAIM_MASK too.

>  
> -	data.pages = (struct page **)__get_free_page(GFP_KERNEL | __GFP_ZERO);
> +	data.pages = (struct page **)__get_free_page(gfp_mask | __GFP_ZERO);
>  	if (!data.pages)
>  		return -ENOMEM;
>  
>  	while (nr_total) {
>  		nr_pages = min(nr_total, PAGE_SIZE / sizeof(data.pages[0]));
> -		ret = ___alloc_pages_bulk(data.pages, nr_pages);
> +		ret = ___alloc_pages_bulk(data.pages, nr_pages, gfp_mask);
>  		if (ret)
>  			break;
>  
>  		data.start = start;
> +		if (noblock)
> +			flags = memalloc_noreclaim_save();
> +


This should be the same as in __vmalloc_area_node():

	if (noblock)
		flags = memalloc_noreclaim_save();
	else if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
 		flags = memalloc_nofs_save();
 	else if ((gfp_mask & (__GFP_FS | __GFP_IO)) == 0)
 		flags = memalloc_noio_save();


It would be better to fix noio/nofs stuff first with separate patch, as it's
bug and needs cc stable. And add support for noblock in follow up.

It might be a good idea to consolidate such logic in separate function,
memalloc_save(gfp_mask)/memalloc_restore(gfp_mask, flags) ?

>  		ret = apply_to_page_range(&init_mm, start, nr_pages * PAGE_SIZE,
>  					  kasan_populate_vmalloc_pte, &data);
> +		if (noblock)
> +			memalloc_noreclaim_restore(flags);
> +
>  		___free_pages_bulk(data.pages, nr_pages);
>  		if (ret)